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Transcript
Wireless power for mobile phones
System overview
Nov 25, 2012
V1.1
1
System overview
Rx
Tx
• Embedded in mobile device
• After market case/dongle
connected through the
power connector
• Add-on connected through
dedicated WLC pins
• Embedded in
furniture/car/infrastructure
• After market mat
2
Block diagram
Power
Source
Power
Resonance circuit
& power driver
TX
Coil
RX
Coil
Matching circuit
& Rectifier
Control
Unit
Control
Unit
Demodulator
Modulator
Communication
DC/DC
3
Tx-Rx coils
4
Tx-Rx coils – Magnetic induction basics
Electric current flowing in a wire gives rise to a magnetic field around it.
Alternating the current will alternate the magnetic field
Shaping the wire as a loop will band that field in a “lung” shape.
5
Figures: http://ipodphysics.com/magnets-loop-or-coil.phpt
Tx-Rx coils – Magnetic induction basics
Energy coupling means that an energy source has a mean of transferring
its energy to a second object. Transformers may use iron core to deliver
the magnetic flux
Wireless power system is an air core transformer between planar coils
one on top of the other.
Figure 1: http://www.electrical4u.com/what-is-transformer-definition-working-principle-of-transformer/ Figure 2: http://makezine.com/2013/11/04/component-of-the-monthtransformer/ Figure 3: http://www.britannica.com/EBchecked/media/1355/Magnetic-field-B-of-two-current-loops-with-currents-in
6
Tx-Rx coils – Coil designs
Single coil– Most common design
Pros – chip and easy solution / Cons – difficult alignment
Large Tx coil – Common in loosely coupled systems
Pros – easy alignment / Cons – difficult design and tune
Array of small Tx coil – One or more coils provide
power simultaneously
Pros – easy alignment / Cons – Cost of coils and drivers
3 coil array – Only one coil provides power at a time
Pros – easy alignment / Cons – Cost of coils and drivers
7
Fig1:http://www.qitah.com/blog.htmlFig2:http://phys.org/news203691107.htmlFig3:http://patentimages.storage.googleapis.com/US20130119773A1/US20130119773A1-20130516-D00015.png
Resonance circuit and power driver
8
Resonance circuit and power driver
Power driver
Resonance circuit
Resonant circuit - Determines the self resonance frequency of the Tx,
Mainly influenced by the coil and the resonance capacitors.
Power driver - pushes the current to the resonance circuit in different
frequencies around the self resonance
9
Figure 1: HIGH EFFICIENCY LOOSELY COUPLED WIRELESS POWER TRANSFER SYSTEM VIA MAGNETIC INDUCTION By ZHEN NING LOW
Resonance circuit
• The overall impedance the driver “sees” when modeled as a series RLC circuit
• At the resonance frequency the capacitive and inductive impedance equals
Amplitude
The driver then sees resistive only minimum overall impedance and the power
delivery to the Rx is maximal
Frequency
• The resonance curve changes with each different :
 Rx design (EE & ME)
 Phone material
 Misalignment from the center
 Variation during manufacturing
 Load drawn
Figure 1: http://perlgeek.de/blog-en/perl-6/rakudo-memory-leaks.html
10
Driving the power
Amplitude
Frequency control – the driver changes the frequency along the resonance curve
 Control becomes difficult when Q is high & at resonance control is unstable
 Frequency range shall be dynamic due to curve changes
 Passing to the second side of the peak may reverse the control rules
Frequency
Other methods of control:
Voltage control – increasing the input voltage will increase the current
through the coil and the transmitted power
Pulse width control – increasing the on time of the signal will increase the
transmitted power
11
Data modulation
12
Data modulation
Power
driver
Modulator
Matching
circuit &
Rectifier
Demodulator
load modulation • Rx modulates the operational frequency by short circuiting the coil
to a secondary load
• The secondary load changes both the load of the Tx and the
resonance curve
• The demodulator sense the change in voltage, current or phase
between them on the operational frequency
13
Data modulation
Example of voltage change at the Tx
Example of phase change at the Tx
Signals in reality may vary a lot from the simulation presented….
14
Questions? Comments? Remarks?
It’s called wireless
power, it’s the future
Thanks,
Rotem Shraga
([email protected] ; 052-6443944)
Figure: http://www.fodrizzle.com/wp-content/uploads/2012/02/funny-birds-wire-drawing.jpg
15